good point, not sure about the invasion of britain, i think thats a hard one to call, i suspect that any invasion would ultimately have faile. though the nazi's might have gained a foothold, they would have suffered massive losses in shipping, casuing huge destruction to their supply lines, essentially the problem faced in russia, but exacerbated by the need to cart things acroos the channel.
Saying that there are arguements on both sides to approve or disapprove the hypothesis.
As it stands though i would say that stalingrad, or launching the drive to stalingrad was the mistake, perhaps more in that it alientaed the wehrmacht high command from hitlers lunacy, making a division between politcs and army that was not recovered from.
One interesting thing i've been considering though is that if we pick one moment as the defintitve point (say D-Day for sake of arguement and because im wathcing the longest day)
What was the decisive moment in that battle/campaign. and so in turn can we pinpoint the deciseve action by thei individual or small rgoup of individuals that was the turning point? or is this just a for want of nail arguement?